Proposed design ( pending )

[larsmith]

Here's my ( incomplete ) rocket heater design, without a 55 gal drum heat exchanger, which has been replaced with a mass of fire brick which I acquired inexpensively ( a dollar a brick ).

This heater has three exhaust channels, two of which run each side of the heat riser and one which runs down the back. The channels are approx 6.5" X 2.5" ( plus thickness of fire brick mortar ). My goal has been to keep as much heat in the brick as possible, exhausts contributing to the heat of the heat riser and hopefully contributing to it's burn efficiency.

I expect to line the outside of the rocket with tradtional red brick.

I've more of a demand for consistant heat than I do of instant heat so am considering building the rocket without the barrel.

I've yet to come up with a final design for the final exhaust channels to exit the room ...

And that's where this thread comes in.

My fire brick are 2.5" by 4.5" by (almost) 9" and are approx 7lbs a piece. In the picture, you can see the traditional rocket "J" shape in the center, flanked by each of the three exhaust channels, which I've strategically colored differently so that you can tell what's there.

I've removed the "lid" so that you can get a 3-D effect of "looking down" part way into the channels.

My question is ... "How much more mass should I need to provide in order to consume as much of the heat as possible while at the same time leaving enough heat exiting the building to avoid the concerns about condensation in any pipes I use to exit the building ?

Presently, I've considered using "sidewalk pavers" as a foundation / pad for my rocket heater, instead of having to mix / pour a cement pad. Do you think I can safely proceed with this, with a reasonable expectation that the pavers will provide adequate footing for the heater ? Or should I consider some other approach. Presently the floor of my heater room ( which I'm just finishing up now, as I've just added it to the side of my house ) is sand / clay only and I plan to leave it that way, if possible.

picasaweb.google.com/larsmith217/RocketHeater#

Keep checking back because I've been working on this design off and on today ... and as of 9:17 Eastern time here in the US of A, Just finished adding a few more images of the design, broken down so you can see some of the details.

[canyon]

WOW! You guys doing these awesome 3d graphics blow me away! The all brick approach is interesting. As obvious as your graphics are for seeing everything, I'm kind of confused on the ash collection area after the three channel down flow. Is there an area of sufficient volume to collect the ash and a clean out? I'm also ignorant as to what a sidewalk paver is. If it is urbanite (actual sidewalk section) I would think that would make a good foundation but I would want to heavily pack/tamp gravel/sand after excavating a little of your clay/sand floor for under it. As to the amount of mass following your rocket I think that Donkey has made a good suggestion on a prior post about adding mass/length with the stove operating until you just start seeing steam or the exit stack temp you are looking for. Then maybe a little more for once the whole thing is cured/dry. Anyway, just my two cents and admiration.

[Donkey]

First thing I'm seeing: the heat riser DOES need to be insulated from the rest. It will perform better, get up to heat faster and burn cleaner overall.
I can't really answer the "how much mass" question.. It all depends and as far as I know, no one's pinned down any kind of kilograms per calorie or some such ratio.. I'd say, if you can try different configurations till you hit on the balance that works best for your situation.

The pavers should work, assuming they sit on a firm base that won't shift over time or be exposed to too much heat. Sand is good, though you need some way of being sure it will stay in place. If it shifts around, your stove could settle un-evenly and come apart or develop cracks in bad places.

Have you considered peterberg's bell stove concept? looks like you got the bricks to do it and it greatly simplifies building and cleaning. You can still use the standard down-feed box as in your design. That bell should be extremely good at spreading heat evenly over the entire stove body.
If you haven't seen it yet, check his thread here.

[larsmith]

Credit where credit is due ... anyone who has adequate access to the internet can download / install for free the program called SketchUp by going to SketchUp.Google.com

Sidewalk pavers are poured pieces of concrete that are about 2" thick and approx 2'X2' square and are laid down on front yards, side entrances, in gardens, etc. as sidewalk "stepping stones" so to speak. Some are "molded" in the sense that on top, they look like laid brick from old city road ways, etc. In other words, some sidewalk pavers are more "decorative" than more commonly poured concrete city sidewalks.

As for the Ash Collection / Cleanout ... that's likely to be the next phase of my design, followed by my (probably) all-red-brick heat battery / exhaust channels running over to my final exit pipes.

After reading Donkey's comment "First thing I'm seeing: the heat riser DOES need to be insulated from the rest. It will perform better, get up to heat faster and burn cleaner overall. "

I'm curious how long it takes an all firebrick or soapstone russian or siberian or finnish masonry heater to come up to temp for efficient burning. Due to some safety concerns ( family and community ) I'm presently opting to not use the 55 Gal barrel. ( others who've heard of it being part of my design are not nearly as convinced as I am of its safety ... so to keep the peace, I'm opting for the all-brick approach ).

If anyone knows how I might determine how long I can expect my heater to come up to an efficient temp, let me know.

Something to know as you consider your answer ... my heat riser has 2.5" thickness on all sides. There are three exhaust channels which flow down the "outer" surface of the heat riser, lending their heat to the temperature of the heat riser, thus contributing to it coming up to temp more quickly ( potentially more quickly than the Bell Design being discussed in the other thread )

Since I'm more concerned with long-lasting heat than I am in "sudden" heat, I like the potential of the design I've posted at the link mentioned above, due to what I've read about masonry heaters.

Now I need to discover the pro's / con's of steel heat riser and of firebrick heat risers accompanied with heat exhaust channels on three sides of the heat riser, as in the design linked to above.

As a P.S. ... where's the server on which this Forum is hosted ? I've noticed the Posted Times being way off my local time ... like over four hours behind, which kinda puts the server off shore somewhere west of where I am in eastern USA.

[Donkey]

.. Heat always flows from hotter to colder. Seems obvious at first glance, yes?
Though it may seem counter-intuitive, the heat riser will (when the fire is burning) always be hotter than the gasses flowing down the outside of the pipe. Allowing easy heat transfer between the two can ONLY serve to cool the heat riser.

The difference between steel pipe and brick?? Brick is easier to find than a good length of pipe..
The less mass you have between the insulation and the flame, the faster the works will get up to heat. 1/4" steel pipe is very conductive and compared to brick, has far less thermal mass to heat. Less time to heat up, less energy stolen from the system early on.

[larsmith]

Donkey stated "Heat always flows from hotter to colder ... (edited) ... Though it may seem counter-intuitive, the heat riser will (when the fire is burning) always be hotter than the gasses flowing down the outside of the pipe. Allowing easy heat transfer between the two can ONLY serve to cool the heat riser.

The brick takes time to heat thru from inside to out. Wouldn't the exhaust heat gasses, during the initial moments after ignition, be likely to heat up the "outside" of the heat riser faster than the heat being conducted thru the brick from the inside ? I'm aware that my ignorance / lack of experience may be tripping me up here but I was thinking that the exhaust gasses would serve to heat the brick thru faster as they pass down the exhaust channels, thus getting the heat riser up to a more efficient temperature faster than if I just vented the gasses out from the heat riser to, say, a cob bench, etc.

Donkey, do I understand you to be saying (above) that the faster the temp gets up in the rocket, the more efficiently the gasses are burned, thus resulting in more heat created instead of inefficiently ( ie: only partially ) burned gasses venting out of a system & heat thus being lost ?

( I just updated the Rocket Heater photo album so that more detail is shown for the secondary combustion area of the heater to be more easily seen / understood ) PicasaWeb.google.Com/LARSmith217

[chronictom]

I think the point you are missing is related to the thermal mass question I was asking elsewhere...

Due to the lack of thermal mass in the riser itself, it gets up to temperature almost instantly, and from the point of the final burn (or re-burn), it gets cooler. The faster it gets up to temperature, the less unburnt gases escape, resulting in an increased efficiency over a slow build up.

Subject to verification by donkey of course... lol

[Donkey]

... Yes, I suppose the riser would get up to heat a little faster with heat flowing down the outside. Though it may not be much faster and only up to a point.. From that point onward it would sap heat from the system.
How much and how critical it all is I'm not sure.
It could be that everything would work just fine for all time without insulation.. It could be otherwise.. Better to insulate and be happy.
Seems better to be cautious in this rather than have to take the works apart and start over.
Unless yer game for the experiment and don't mind the possibility.. I am curious to know, though can't advise you to be rash for my curiosities sake.